Modular instrument systems permit a variety of different electronic instruments to be installed and interconnected in a single chassis. To create a customized system of test, measurement, and analysis equipment, such as for automated testing, a user selects the required modules, and installs them in a chassis that provides power, cooling, and functional electronic interconnection between the modules. Typically, the chassis is in the form of a cabinet with a large front aperture in which modules may be inserted side-by-side in the manner of books on a bookshelf. An example of such a system is a VXI (VME Extension for Instrumentation) test chassis using the VXIbus standard.
Ventilation of all the modules is provided by the chassis. In existing systems, each module has a housing through which air may flow for cooling, with perforated or open top and bottom panels permitting vertical air flow through the module. The chassis includes a fan that blows air from a plenum below all the modules to an exhaust plenum above the modules.
For many applications, a user may not require as many instrument modules as there are available slots in the chassis. However, when one or more slots are empty, much of the cooling air follows the path of least resistance through the empty slots, leaving the installed modules inadequately ventilated. To avoid this impairment of cooling, existing systems provide solid dummy modules that block the flow of air. When dummy modules are installed in all open slots in the chassis, air flow is directed only through the functional modules. However, dummy modules may be inadvertently omitted, particularly as systems are reconfigured for different later uses by different personnel unaware of the importance of the dummy modules. Also, when not in use, the dummy modules require storage space that may not be available nearby the location of the system.
The embodiment disclosed herein overcomes these disadvantages by providing a modular instrumentation system with a chassis having a number of module slots and having a plenum providing airflow to the slots. A ventilator connected to the chassis blows air into the plenum. A number of dampers are connected to the chassis, each adjacent to a respective module slot and movable between a closed position blocking airflow between the plenum and the module slot, and an open position permitting airflow between the plenum and the module slot. Each damper is biased to the closed position and automatically moves to the open position in response to installation of a module in the module slot.